Many electronic systems rely on the use of boosted voltages in excess of a given supply voltage. For example, micro-electromechanical systems (MEMS) may use boosted voltage to bias a proof mass to improve the sensitivity of a MEMS sensor. In some cases, a boosted voltage may be used to supply a high-voltage driver to allow for application of increased electrostatic force to actuate a MEMS device.
A class of voltage boosters known as charge pumps provides elevated voltage depositing charge onto storage capacitors arranged in a sequential chain of individual pumping stages. Voltage is boosted to increasing levels along the chain, and voltages well in excess of the input supply can be produced. Desirable characteristics of charge pumps include low parasitics, high pumping efficiency and low ripple. It is also desirable to be able to generate large voltages without exceeding the breakdown voltage of the devices used in the charge pump chain. For compatibility with low-cost manufacturing processes, it is sometimes desirable to have charge pumps in which devices with comparatively low breakdown voltages may nonetheless be used in the individual pumping stages to produce very large output voltages. For example, in some situations it may be desirable to produce a bias voltage in excess of 20V using devices rated to only 2V. In such cases, a large number of stages may be employed to achieve the required voltage boosting ratio. Thus, to further minimize cost, it is desirable to minimize the number of components required for the individual charge pump stages.
Thus, there is a need for charge pumps providing high efficiency and low ripple in a manner compatible with the use of relatively low breakdown voltage components wherein the number of components required for each pumping stage is minimized. The present invention addresses such a need.